Question

我想编写一个C程序，该程序将文件夹的路径作为参数并显示有关其包含的文件的信息。

到目前为止，我已经写了这个：

select -- your third query here
from (
  select ... -- your first query
) step1,
(
  select ... -- your second query
) step2

哪个可以编译，但是#include <sys/types.h> #include <sys/stat.h> #include <dirent.h> #include <stdio.h> #include <string.h> int main(int argc, char** argv){ char* dir_path = argv[1]; char* dir_path_bar = strcat(dir_path, "/"); DIR* dir = opendir(dir_path); for(struct dirent* entry = readdir(dir); entry != NULL; entry = readdir(dir)){ printf("Next entry is %s\n", entry->d_name); char* entry_path = strcat(dir_path_bar, entry->d_name); printf("%s\n", entry_path); struct stat buf; stat(entry_path, &buf); printf("Its inode number is %s\n", entry->d_ino); printf("Its inode number is %s\n", buf.st_ino); printf("Its uid is %s\n", buf.st_uid); printf("Its size is %s bytes\n", buf.st_size); }; closedir(dir); }调用给了我SEGFAULT。发生了什么事？

Answer 1

两个问题：

您正在将追加连续添加到输入（argv[1]）参数，该参数的行为不确定。您不能将字符串追加到argv的字符串中。
也使用未定义的%s打印整数值。 % s需要一个char *参数，但您想打印整数值。

您可以改为使用临时缓冲区并将其传递给stat(2)：

#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <limits.h>
#include <stdlib.h>

int main(int argc, char** argv)
{
    if (argc != 2) {
        printf("Usage: %s dir\n", argv[0]);
        exit(1);
    }

    char* dir_path = argv[1];
    DIR* dir = opendir(dir_path);

    if (!dir) {
        perror("opendir");
        exit(1);
    }

    for(struct dirent* entry = readdir(dir); entry != NULL; entry = readdir(dir)) {
        char entry_path[PATH_MAX] = {0};
        int rc = snprintf(entry_path, sizeof entry_path, "%s/%s", dir_path, entry->d_name);

        if ( rc < 0 || rc >= sizeof entry_path) {
            fprintf(stderr, "Path truncated for '%s'\n", entry->d_name);
            continue;
        }
        printf("Next entry is: %s\n", entry_path);
        struct stat buf;
        if (stat(entry_path, &buf) == 0) {
            printf("Its inode number is %ju\n", (uintmax_t)entry->d_ino);
            printf("Its inode number is %ju\n", (uintmax_t)buf.st_ino);
            printf("Its uid is %jd\n", (intmax_t)buf.st_uid);
            printf("Its size is %jd bytes\n", (intmax_t)buf.st_size);
        } else {
            perror("stat");
        }
    }

    closedir(dir);
}

我还添加了一些错误检查。

Answer 2

正如其他人所述，您不能附加到argv[1]。您不能在循环内继续添加它。而且，您不能使用%s输出数字。

这是您的代码，其中的错误已注解并修复了[使用#if 0显示旧代码]：

#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int
main(int argc, char **argv)
{
    char *dir_path = argv[1];

// NOTE/BUG: argv[1] has a fixed size you can't append to it
#if 0
    char *dir_path_bar = strcat(dir_path, "/");
#else
    char dir_path_bar[PATH_MAX];
    strcpy(dir_path_bar,dir_path);
    strcat(dir_path_bar,"/");
#endif

    DIR *dir = opendir(dir_path);
#if 1
    if (dir == NULL) {
        perror(dir_path);
        exit(1);
    }
#endif

    for (struct dirent *entry = readdir(dir); entry != NULL;
        entry = readdir(dir)) {
        printf("Next entry is %s\n", entry->d_name);

// NOTE/BUG: because you don't reset dir_path_bar, this just keeps appending
// to it
#if 0
        char *entry_path = strcat(dir_path_bar, entry->d_name);
#else
        char entry_path[PATH_MAX];
        strcpy(entry_path,dir_path_bar);
        strcat(entry_path,entry->d_name);
#endif

        printf("\n");
        printf("%s\n", entry_path);
        struct stat buf;

        stat(entry_path, &buf);

// NOTE/BUG: these need one or more of: %d/%ld/%lld (vs %s)
#if 0
        printf("Its inode number is %s\n", entry->d_ino);
        printf("Its inode number is %s\n", buf.st_ino);
        printf("Its uid is %s\n", buf.st_uid);
        printf("Its size is %s bytes\n", buf.st_size);
#else
        printf("Its inode number is %ld\n", entry->d_ino);
        printf("Its inode number is %ld\n", buf.st_ino);
        printf("Its uid is %d\n", buf.st_uid);
        printf("Its size is %ld bytes\n", buf.st_size);
#endif
    };

    closedir(dir);

    return 0;
}

Answer 3

在其他两个较早的答案中未显示，这很好地避免了过度复制。

形成entry_path时，仅需要覆盖条目本身，而不是整个字符串。这对于带有较长的固定目录字符串非常有用。

    dir_path_len = strlen(dir_path);
    if (dir_path_len >= PATH_MAX - 1) { return EXIT_FAILURE; } // too long

    char entry_path[PATH_MAX];
    strcpy(entry_path, dir_path);
    strcpy(entry_path + dir_path_len++, "/"); // Can use strcpy() here

    DIR *dir = opendir(dir_path);
    ...
    for (struct dirent *entry = readdir(dir); entry != NULL; entry = readdir(dir)) {
        printf("Next entry is %s\n", entry->d_name);

        entry_len = strlen(entry->d_name);
        if (dir_path_len + entry_len >= PATH_MAX) { 
            continue;
            // or 
            return EXIT_FAILURE; // too long
        }
        strcpy(path + dir_path_len, entry->d_name);  // strcpy(), not strcat()

        printf("\n%s\n", entry_path);

        struct stat buf;
        if (stat(entry_path, &buf) ...
        ...

遍历目录并打印一些信息

3 个答案: